Wearable cardioverter defibrillator (WCD) system computing patient heart rate by multiplying ECG signals from different channels

ABSTRACT

A wearable cardioverter defibrillator system includes a support structure that is configured to be worn by a patient. When thus worn, the support structure may attach electrodes at different locations of the patient&#39;s body, so as to define different vectors. A measurement circuit may sense ECG signals from the different vectors substantially concurrently. A processor may multiply together these substantially concurrent ECG signals to derive a product waveform. The processor may then detect peaks in the product waveform, measure durations of time intervals between successive peaks, and determine the patient&#39;s heart rate from these durations. An advantage can be that the heart rate may be computed notwithstanding noise in the individual ECG signals.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a Continuation In Part of copending U.S.patent application Ser. No. 15/920,505, filed on Mar. 14, 2018, andfurther claims priority from U.S. Provisional Patent Application Ser.No. 62/483,761, filed on Apr. 10, 2017.

BACKGROUND

When people suffer from some types of heart arrhythmias, the result maybe that blood flow to various parts of the body is reduced. Somearrhythmias may even result in a Sudden Cardiac Arrest (SCA). SCA canlead to death very quickly, e.g. within 10 minutes, unless treated inthe interim.

Some people have an increased risk of SCA. People at a higher riskinclude patients who have had a heart attack, or a prior SCA episode. Afrequent recommendation is for these people to receive an ImplantableCardioverter Defibrillator (ICD). The ICD is surgically implanted in thechest, and continuously monitors the patient's electrocardiogram (ECG).If certain types of heart arrhythmias are detected, then the ICDdelivers an electric shock through the heart.

After being identified as having an increased risk of an SCA, and beforereceiving an ICD, these people are sometimes given a WearableCardioverter Defibrillator (WCD) system. (Early versions of such systemswere called wearable cardiac defibrillator systems.) A WCD systemtypically includes a harness, vest, or other garment that the patient isto wear. The WCD system further includes electronic components, such asa defibrillator and electrodes, coupled to the harness, vest, or othergarment. When the patient wears the WCD system, the external electrodesmay then make good electrical contact with the patient's skin, andtherefore can help sense the patient's ECG. If a shockable heartarrhythmia is detected, then the defibrillator delivers the appropriateelectric shock through the patient's body, and thus through the heart.

A challenge in the prior art is that the patient's ECG signal may becorrupted by electrical noise. As such, it can be hard to interpret theECG signal.

All subject matter discussed in this Background section of this documentis not necessarily prior art, and may not be presumed to be prior artsimply because it is presented in this Background section. Plus, anyreference to any prior art in this description is not, and should not betaken as, an acknowledgement or any form of suggestion that such priorart forms parts of the common general knowledge in any art in anycountry. Along these lines, any recognition of problems in the prior artdiscussed in this Background section or associated with such subjectmatter should not be treated as prior art, unless expressly stated to beprior art. Rather, the discussion of any subject matter in thisBackground section should be treated as part of the approach takentowards the particular problem by the inventor. This approach in and ofitself may also be inventive.

BRIEF SUMMARY

The present description gives instances of wearable cardioverterdefibrillator (WCD) systems, storage media that store programs, andmethods, the use of which may help overcome problems and limitations ofthe prior art.

In embodiments, a wearable cardioverter defibrillator system includes asupport structure that is configured to be worn by a patient. When thusworn, the support structure may attach electrodes at different locationsof the patient's body, so as to define different vectors. A measurementcircuit may sense ECG signals from the different vectors substantiallyconcurrently. A processor may multiply together these substantiallyconcurrent ECG signals to derive a product waveform. The processor maythen detect peaks in the product waveform, measure durations of timeintervals between successive peaks, and determine the patient's heartrate from these durations. An advantage can be that the heart rate maybe computed notwithstanding noise in the individual ECG signals.

These and other features and advantages of the claimed invention willbecome more readily apparent in view of the embodiments described andillustrated in this specification, namely in this written specificationand the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of components of a sample wearable cardioverterdefibrillator (WCD) system, made according to embodiments.

FIG. 2 is a diagram showing sample components of an externaldefibrillator, such as the one belonging in the system of FIG. 1, andwhich is made according to embodiments.

FIG. 3 is a conceptual diagram for illustrating how different electrodesmay sense ECG signals of the patient along different vectors accordingto embodiments.

FIG. 4 shows time diagrams that illustrate sample generalized noisy ECGsignals, their product waveform, and how that product waveform may beused to determine the patient's heart rate according to embodiments.

FIG. 5A is a time diagram of two sample noise-free ECG signals fromdifferent vectors, superimposed according to embodiments.

FIG. 5B is a time diagram of noisy versions of the ECG signals of FIG.5A.

FIG. 5C is a time diagram of a product waveform of the ECG signals ofFIG. 5B according to embodiments.

FIG. 6A is a time diagram of two sample noise-free ECG signals fromdifferent vectors, superimposed according to embodiments.

FIG. 6B is a time diagram of noisy versions of the ECG signals of FIG.6A.

FIG. 6C is a time diagram of a product waveform of the ECG signals ofFIG. 6B according to embodiments.

FIG. 7 is a time diagram of a product waveform that can be derived bymultiplying the product waveform of FIG. 5C with the product waveform ofFIG. 6C according to embodiments.

FIG. 8 is a time diagram for illustrating how peaks may be detected in asample product waveform according to embodiments with a fixed detectionthreshold.

FIG. 9 is a time diagram for illustrating how peaks may be detected in asample product waveform according to embodiments with a variabledetection threshold.

FIG. 10 is a diagram for illustrating an example of why ECG signals ofthe patient sensed along different vectors according to embodiments maybe initially unsynchronized.

FIG. 11 shows time diagrams for illustrating how ECG signals fromdifferent channels can become synchronized according to embodiments.

FIG. 12 is a flowchart for illustrating methods according toembodiments.

FIG. 13 is a time diagram for illustrating time relationships amongvarious ECG signals from various channels in a sample contingencyaccording to embodiments.

DETAILED DESCRIPTION

As has been mentioned, the present description is about wearablecardioverter defibrillator (WCD) systems, and related storage media,programs and methods. Embodiments are now described in more detail.

A wearable cardioverter defibrillator (WCD) system made according toembodiments has a number of components. These components can be providedseparately as modules that can be interconnected, or can be combinedwith other components, etc.

FIG. 1 depicts a patient 82. Patient 82 may also be referred to as aperson and/or wearer, since the patient is wearing components of the WCDsystem. Patient 82 is ambulatory, which means patient 82 can walkaround, and is not necessarily bed-ridden.

FIG. 1 also depicts components of a WCD system made according toembodiments. One such component is a support structure 170 that iswearable by patient 82. It will be understood that support structure 170is shown only generically in FIG. 1, and in fact partly conceptually.FIG. 1 is provided merely to illustrate concepts about support structure170, and is not to be construed as limiting how support structure 170 isimplemented, or how it is worn.

Support structure 170 can be implemented in many different ways. Forexample, it can be implemented in a single component or a combination ofmultiple components. In embodiments, support structure 170 could includea vest, a half-vest, a garment, etc. In such embodiments such items canbe worn similarly to parallel articles of clothing. In embodiments,support structure 170 could include a harness, one or more belts orstraps, etc. In such embodiments, such items can be worn by the patientaround the torso, hips, over the shoulder, etc. In embodiments, supportstructure 170 can include a container or housing, which can even bewaterproof. In such embodiments, the support structure can be worn bybeing attached to the patient by adhesive material, for example as shownin U.S. Pat. No. 8,024,037. Support structure 170 can even beimplemented as described for the support structure of US Pat. App. No.US2017/0056682, which is incorporated herein by reference. Of course, insuch embodiments, the person skilled in the art will recognize thatadditional components of the WCD system can be in the housing of asupport structure instead of being attached externally to the supportstructure, for example as described in the US2017/0056682 document.There can be other examples.

A WCD system according to embodiments is configured to defibrillate apatient who is wearing it, by delivering an electrical charge to thepatient's body in the form of an electric shock delivered in one or morepulses. FIG. 1 shows a sample external defibrillator 100, and sampledefibrillation electrodes 104, 108, which are coupled to externaldefibrillator 100 via electrode leads 105. Defibrillator 100 anddefibrillation electrodes 104, 108 can be coupled to support structure170. As such, many of the components of defibrillator 100 could betherefore coupled to support structure 170. When defibrillationelectrodes 104, 108 make good electrical contact with the body ofpatient 82, defibrillator 100 can administer, via electrodes 104, 108, abrief, strong electric pulse 111 through the body. Pulse 111 is alsoknown as shock, defibrillation shock, therapy and therapy shock. Pulse111 is intended to go through and restart heart 85, in an effort to savethe life of patient 82. Pulse 111 can further include one or more pacingpulses, and so on.

A prior art defibrillator typically decides whether to defibrillate ornot based on an ECG signal of the patient. However, externaldefibrillator 100 may initiate defibrillation (or hold-offdefibrillation) based on a variety of inputs, with ECG merely being oneof them.

Accordingly, it will be appreciated that signals such as physiologicalsignals containing physiological data can be obtained from patient 82.While the patient may be considered also a “user” of the WCD system,this is not a requirement. That is, for example, a user of the wearablecardioverter defibrillator (WCD) may include a clinician such as adoctor, nurse, emergency medical technician (EMT) or other similarlysituated individual (or group of individuals). The particular context ofthese and other related terms within this description should beinterpreted accordingly.

The WCD system may optionally include an outside monitoring device 180.Device 180 is called an “outside” device because it could be provided asa standalone device, for example not within the housing of defibrillator100. Device 180 can be configured to sense or monitor at least one localparameter. A local parameter can be a parameter of patient 82, or aparameter of the WCD system, or a parameter of the environment, as willbe described later in this document. Device 180 may include one or moretransducers or sensors that are configured to render one or morephysiological inputs or signals from one or more patient parameters thatthey sense.

Optionally, device 180 is physically coupled to support structure 170.In addition, device 180 can be communicatively coupled with othercomponents, which are coupled to support structure 170. Suchcommunication can be implemented by a communication module, as will bedeemed applicable by a person skilled in the art in view of thisdescription.

FIG. 2 is a diagram showing components of an external defibrillator 200,made according to embodiments. These components can be, for example,included in external defibrillator 100 of FIG. 1. The components shownin FIG. 2 can be provided in a housing 201, which may also be referredto as casing 201.

External defibrillator 200 is intended for a patient who would bewearing it, such as patient 82 of FIG. 1. Defibrillator 200 may furtherinclude a user interface 280 for a user 282. User 282 can be patient 82,also known as wearer 82. Or, user 282 can be a local rescuer at thescene, such as a bystander who might offer assistance, or a trainedperson. Or, user 282 might be a remotely located trained caregiver incommunication with the WCD system.

User interface 280 can be made in a number of ways. User interface 280may include output devices, which can be visual, audible or tactile, forcommunicating to a user by outputting images, sounds or vibrations.Images, sounds, vibrations, and anything that can be perceived by user282 can also be called human-perceptible indications. There are manyexamples of output devices. For example, an output device can be alight, or a screen to display what is sensed, detected and/or measured,and provide visual feedback to rescuer 282 for their resuscitationattempts, and so on. Another output device can be a speaker, which canbe configured to issue voice prompts, beeps, loud alarm sounds and/orwords to warn bystanders, etc.

User interface 280 may further include input devices for receivinginputs from users. Such input devices may additionally include variouscontrols, such as pushbuttons, keyboards, touchscreens, one or moremicrophones, and so on. An input device can be a cancel switch, which issometimes called an “I am alive” switch or “live man” switch. In someembodiments, actuating the cancel switch can prevent the impendingdelivery of a shock.

Defibrillator 200 may include an internal monitoring device 281. Device281 is called an “internal” device because it is incorporated withinhousing 201. Monitoring device 281 can sense or monitor patientparameters such as patient physiological parameters, system parametersand/or environmental parameters, all of which can be called patientdata. In other words, internal monitoring device 281 can becomplementary or an alternative to outside monitoring device 180 ofFIG. 1. Allocating which of the parameters are to be monitored by whichof monitoring devices 180, 281 can be done according to designconsiderations. Device 281 may include one or more transducers orsensors that are configured to render one or more physiological inputsfrom one or more patient parameters that it senses.

Patient parameters may include patient physiological parameters. Patientphysiological parameters may include, for example and withoutlimitation, those physiological parameters that can be of any help indetecting by the wearable defibrillation system whether the patient isin need of a shock, plus optionally their medical history and/or eventhistory. Examples of such parameters include the patient's ECG, bloodoxygen level, blood flow, blood pressure, blood perfusion, pulsatilechange in light transmission or reflection properties of perfusedtissue, heart sounds, heart wall motion, breathing sounds and pulse.Accordingly, monitoring devices 180, 281 may include one or more sensorsconfigured to acquire patient physiological signals. Examples of suchsensors or transducers include electrodes to detect ECG data, aperfusion sensor, a pulse oximeter, a device for detecting blood flow(e.g. a Doppler device), a sensor for detecting blood pressure (e.g. acuff), an optical sensor, illumination detectors and sensors perhapsworking together with light sources for detecting color change intissue, a motion sensor, a device that can detect heart wall movement, asound sensor, a device with a microphone, an SpO₂ sensor, and so on. Inview of this disclosure, it will be appreciated that such sensors canhelp detect the patient's pulse, and can therefore also be called pulsedetection sensors, pulse sensors, and pulse rate sensors. Pulsedetection is also taught at least in Physio-Control's U.S. Pat. No.8,135,462, which is hereby incorporated by reference in its entirety. Inaddition, a person skilled in the art may implement other ways ofperforming pulse detection. In such cases, the transducer includes anappropriate sensor, and the physiological input is a measurement by thesensor of that patient parameter. For example, the appropriate sensorfor a heart sound may include a microphone, etc.

In some embodiments, the local parameter is a trend that can be detectedin a monitored physiological parameter of patient 282. A trend can bedetected by comparing values of parameters at different times.Parameters whose detected trends can particularly help a cardiacrehabilitation program include: a) cardiac function (e.g. ejectionfraction, stroke volume, cardiac output, etc.); b) heart ratevariability at rest or during exercise; c) heart rate profile duringexercise and measurement of activity vigor, such as from the profile ofan accelerometer signal and informed from adaptive rate pacemakertechnology; d) heart rate trending; e) perfusion, such as from SpO₂ orCO₂; f) respiratory function, respiratory rate, etc.; g) motion, levelof activity; and so on. Once a trend is detected, it can be storedand/or reported via a communication link, along perhaps with a warning.From the report, a physician monitoring the progress of patient 282 willknow about a condition that is either not improving or deteriorating.

Patient state parameters include recorded aspects of patient 282, suchas motion, posture, whether they have spoken recently plus maybe alsowhat they said, and so on, plus optionally the history of theseparameters. Or, one of these monitoring devices could include a locationsensor such as a Global Positioning System (GPS) location sensor. Such asensor can detect the location, plus a speed can be detected as a rateof change of location over time. Many motion detectors output a motionsignal that is indicative of the motion of the detector, and thus of thepatient's body. Patient state parameters can be very helpful innarrowing down the determination of whether SCA is indeed taking place.

A WCD system made according to embodiments may include a motiondetector. In embodiments, a motion detector can be implemented withinmonitoring device 180 or monitoring device 281. Such a motion detectorcan be made in many ways as is known in the art, for example by using anaccelerometer. In this example, a motion detector 287 is implementedwithin monitoring device 281.

A motion detector of a WCD system according to embodiments can beconfigured to detect a motion event. In response, the motion detectormay render or generate, from the detected motion event or motion, amotion detection input that can be received by a subsequent device orfunctionality. A motion event can be defined as is convenient, forexample a change in motion from a baseline motion or rest, etc. In suchcases, a sensed patient parameter is motion.

System parameters of a WCD system can include system identification,battery status, system date and time, reports of self-testing, recordsof data entered, records of episodes and intervention, and so on.

Environmental parameters can include ambient temperature and pressure.Moreover, a humidity sensor may provide information as to whether it islikely raining. Presumed patient location could also be considered anenvironmental parameter. The patient location could be presumed, ifmonitoring device 180 or 281 includes a GPS location sensor as per theabove, and if it is presumed that the patient is wearing the WCD system.

Defibrillator 200 typically includes a defibrillation port 210, such asa socket in housing 201. Defibrillation port 210 includes electricalnodes 214, 218. Leads of defibrillation electrodes 204, 208, such asleads 105 of FIG. 1, can be plugged into defibrillation port 210, so asto make electrical contact with nodes 214, 218, respectively. It is alsopossible that defibrillation electrodes 204, 208 are connectedcontinuously to defibrillation port 210, instead. Either way,defibrillation port 210 can be used for guiding, via electrodes, to thewearer the electrical charge that has been stored in an energy storagemodule 250 that is described more fully later in this document. Theelectric charge will be the shock for defibrillation, pacing, and so on.

Defibrillator 200 may optionally also have a sensor port 219 in housing201, which is also sometimes known as an ECG port. Sensor port 219 canbe adapted for plugging in sensing electrodes 209, which are also knownas ECG electrodes and ECG leads. It is also possible that sensingelectrodes 209 can be connected continuously to sensor port 219,instead. Sensing electrodes 209 are types of transducers that can helpsense an ECG signal, e.g. a 12-lead signal, or a signal from a differentnumber of leads, especially if they make good electrical contact withthe body of the patient and in particular with the skin of the patient.Sensing electrodes 209 can be attached to the inside of supportstructure 170 for making good electrical contact with the patient,similarly with defibrillation electrodes 204, 208.

Optionally a WCD system according to embodiments also includes a fluidthat it can deploy automatically between the electrodes and thepatient's skin. The fluid can be conductive, such as by including anelectrolyte, for establishing a better electrical contact between theelectrode and the skin. Electrically speaking, when the fluid isdeployed, the electrical impedance between the electrode and the skin isreduced. Mechanically speaking, the fluid may be in the form of alow-viscosity gel, so that it does not flow away from the electrode,after it has been deployed. The fluid can be used for bothdefibrillation electrodes 204, 208, and for sensing electrodes 209.

The fluid may be initially stored in a fluid reservoir, not shown inFIG. 2, which can be coupled to the support structure. In addition, aWCD system according to embodiments further includes a fluid deployingmechanism 274. Fluid deploying mechanism 274 can be configured to causeat least some of the fluid to be released from the reservoir, and bedeployed near one or both of the patient locations, to which theelectrodes are configured to be attached to the patient. In someembodiments, fluid deploying mechanism 274 is activated prior to theelectrical discharge responsive to receiving activation signal AS from aprocessor 230, which is described more fully later in this document.

FIG. 3 is a conceptual diagram for illustrating how electrodes of a WCDsystem may sense or capture ECG signals along different vectorsaccording to embodiments. A section of a patient 382 having a heart 385is shown. There are four electrodes 304, 306, 307, 308, attached todifferent locations of the torso of patient 382, each with a wire lead305. Any pair of these electrodes defines a vector, across which an ECGsignal may be measured. These vectors are also known as channels and ECGchannels. The four electrodes 304, 306, 307, 308 therefore can definesix vectors, across which six respective ECG signals 311, 312, 313, 314,315, 316 can be sensed. FIG. 3 thus illustrates a multi-vectorsituation. In FIG. 3 it will be understood that electrodes 304, 306,307, 308 are drawn on the same plane for simplicity, while that is notnecessarily the case. Accordingly, the vectors of ECG signals 311-316are not necessarily on the same plane, either.

Any one of ECG signals 311-316 might provide sufficient data for makinga shock/no shock determination. The effort is to shock when needed, andnot shock when not needed. The problem is that, at any given point intime, some of these ECG signals may include noise, while others not. Thenoise may be due to patient movement or how well the electrodes contactthe skin. The noise problem for a WCD may be further exacerbated by thedesire to use dry, non-adhesive monitoring electrodes. Dry, non-adhesiveelectrodes are thought to be more comfortable for the patient to wear inthe long term, but may produce more noise than a conventional ECGmonitoring electrode that includes adhesive to hold the electrode inplace and an electrolyte gel to reduce the impedance of theelectrode-skin interface.

FIG. 3 also shows a measurement circuit 320 and a processor 330, whichcan be made as described for measurement circuit 220 and processor 230later in this document. Processor 330 may further compute a heart rate333 according to embodiments, as described in more detail further inthis document.

Returning to FIG. 2, defibrillator 200 also includes a measurementcircuit 220, as one or more of its sensors or transducers. Measurementcircuit 220 can be configured to sense one or more electricalphysiological signals of the patient from sensor port 219, if provided.For instance, measurement circuit 220 can be configured to senseElectrocardiogram (ECG) signals, as measurement circuit 320 can beconfigured to sense ECG signals from different vectors. Even ifdefibrillator 200 lacks sensor port 219, measurement circuit 220 mayoptionally obtain physiological signals through nodes 214, 218 instead,when defibrillation electrodes 204, 208 are attached to the patient. Inthese cases, the physiological input reflects an ECG measurement. Thepatient parameter can be an ECG, which can be sensed as a voltagedifference between electrodes 204, 208. In addition the patientparameter can be an impedance, which can be sensed between electrodes204, 208 and/or the connections of sensor port 219. Sensing theimpedance can be useful for detecting, among other things, whether theseelectrodes 204, 208 and/or sensing electrodes 209 are not making goodelectrical contact with the patient's body. These patient physiologicalsignals can be sensed, when available. Measurement circuit 220 can thenrender or generate information about them as physiological inputs, data,other signals, etc. For instance, signals sensed as voltages can bedigitized to become numbers by an Analog to Digital Converter (ADC). Inembodiments, the signals are sampled at a high frequency, and the resultis simply a group of values—voltage or impedance—as a function of timepassing.

Defibrillator 200 also includes a processor 230. Processor 230 may beimplemented in a number of ways. Such ways include, by way of exampleand not of limitation, digital and/or analog processors such asmicroprocessors and Digital Signal Processors (DSPs); controllers suchas microcontrollers; software running in a machine; programmablecircuits such as Field Programmable Gate Arrays (FPGAs),Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices(PLDs), Application Specific Integrated Circuits (ASICs), anycombination of one or more of these, and so on.

Processor 230 may include, or have access to, a non-transitory storagemedium, such as memory 238 that is described more fully later in thisdocument. Such a memory can have a non-volatile component for storage ofmachine-readable and machine-executable instructions. A set of suchinstructions can also be called a program. The instructions, which mayalso referred to as “software,” generally provide functionality byperforming methods as may be disclosed herein or understood by oneskilled in the art in view of the disclosed embodiments. In someembodiments, and as a matter of convention used herein, instances of thesoftware may be referred to as a “module” and by other similar terms.Generally, a module includes a set of the instructions so as to offer orfulfill a particular functionality. Embodiments of modules and thefunctionality delivered are not limited by the embodiments described inthis document.

Processor 230 can be considered to have a number of modules. One suchmodule can be a detection module 232. Detection module 232 can include aVentricular Fibrillation (VF) detector. The patient's sensed ECG frommeasurement circuit 220, which can be available as physiological inputs,data, or other signals, may be used by the VF detector to determinewhether the patient is experiencing VF. Detecting VF is useful, becauseVF typically results in SCA. Detection module 232 can also include aVentricular Tachycardia (VT) detector, and so on.

Another such module in processor 230 can be an advice module 234, whichgenerates advice for what to do. The advice can be based on outputs ofdetection module 232. There can be many types of advice according toembodiments. In some embodiments, the advice is a shock/no shockdetermination that processor 230 can make, for example via advice module234. The shock/no shock determination can be made by executing a storedShock Advisory Algorithm. A Shock Advisory Algorithm can make a shock/noshock determination from one or more ECG signals that are sensed orcaptured according to embodiments, and determining whether a shockcriterion is met. The determination can be made from a rhythm analysisof the sensed or captured ECG signal or otherwise.

In some embodiments, when the determination is to shock, an electricalcharge is delivered to the patient. Delivering the electrical charge isalso known as discharging. Shocking can be for defibrillation, pacing,and so on.

Processor 230 can include additional modules, such as other module 236,for other functions. In addition, if internal monitoring device 281 isindeed provided, it may be operated in part by processor 230, etc.

Defibrillator 200 optionally further includes a memory 238, which canwork together with processor 230. Memory 238 may be implemented in anumber of ways. Such ways include, by way of example and not oflimitation, volatile memories, Nonvolatile Memories (NVM), Read-OnlyMemories (ROM), Random Access Memories (RAM), magnetic disk storagemedia, optical storage media, smart cards, flash memory devices, anycombination of these, and so on. Memory 238 is thus a non-transitorystorage medium. Memory 238, if provided, can include programs forprocessor 230, which processor 230 may be able to read and execute. Moreparticularly, the programs can include sets of instructions in the formof code, which processor 230 may be able to execute upon reading.Executing is performed by physical manipulations of physical quantities,and may result in functions, operations, processes, actions and/ormethods to be performed, and/or the processor to cause other devices orcomponents or blocks to perform such functions, operations, processes,actions and/or methods. The programs can be operational for the inherentneeds of processor 230, and can also include protocols and ways thatdecisions can be made by advice module 234. In addition, memory 238 canstore prompts for user 282, if this user is a local rescuer. Moreover,memory 238 can store data. This data can include patient data, systemdata and environmental data, for example as learned by internalmonitoring device 281 and outside monitoring device 180. The data can bestored in memory 238 before it is transmitted out of defibrillator 200,or stored there after it is received by defibrillator 200.

Defibrillator 200 may also include a power source 240. To enableportability of defibrillator 200, power source 240 typically includes abattery. Such a battery is typically implemented as a battery pack,which can be rechargeable or not. Sometimes a combination is used ofrechargeable and non-rechargeable battery packs. Other embodiments ofpower source 240 can include an AC power override, for where AC powerwill be available, an energy-storing capacitor, and so on. In someembodiments, power source 240 is controlled by processor 230.Appropriate components may be included to provide for charging orreplacing power source 240.

Defibrillator 200 may additionally include an energy storage module 250.Energy storage module 250 can be coupled to the support structure of theWCD system, for example either directly or via the electrodes and theirleads. Module 250 is where some electrical energy can be storedtemporarily in the form of an electrical charge, when preparing it fordischarge to administer a shock. In embodiments, module 250 can becharged from power source 240 to the desired amount of energy, ascontrolled by processor 230. In typical implementations, module 250includes a capacitor 252, which can be a single capacitor or a system ofcapacitors, and so on. In some embodiments, energy storage module 250includes a device that exhibits high power density, such as anultracapacitor. As described above, capacitor 252 can store the energyin the form of an electrical charge, for delivering to the patient.

Defibrillator 200 moreover includes a discharge circuit 255. When thedecision is to shock, processor 230 can be configured to controldischarge circuit 255 to discharge through the patient the electricalcharge stored in energy storage module 250. When so controlled, circuit255 can permit the energy stored in module 250 to be discharged to nodes214, 218, and from there also to defibrillation electrodes 204, 208, soas to cause a shock to be delivered to the patient. Circuit 255 caninclude one or more switches 257. Switches 257 can be made in a numberof ways, such as by an H-bridge, and so on. Circuit 255 can also becontrolled via user interface 280.

Defibrillator 200 can optionally include a communication module 290, forestablishing one or more wired or wireless communication links withother devices of other entities, such as a remote assistance center,Emergency Medical Services (EMS), and so on. The data can includepatient data, event information, therapy attempted, CPR performance,system data, environmental data, and so on. For example, communicationmodule 290 may transmit wirelessly, e.g. on a daily basis, heart rate,respiratory rate, and other vital signs data to a server accessible overthe internet, for instance as described in US 20140043149. This data canbe analyzed directly by the patient's physician and can also be analyzedautomatically by algorithms designed to detect a developing illness andthen notify medical personnel via text, email, phone, etc. Module 290may also include such interconnected sub-components as may be deemednecessary by a person skilled in the art, for example an antenna,portions of a processor, supporting electronics, outlet for a telephoneor a network cable, etc. This way, data, commands, etc. can becommunicated.

Defibrillator 200 can optionally include other components.

Returning to FIG. 1, in embodiments, one or more of the components ofthe shown WCD system have been customized for patient 82. Thiscustomization may include a number of aspects. For instance, supportstructure 170 can be fitted to the body of patient 82. For anotherinstance, baseline physiological parameters of patient 82 can bemeasured, such as the heart rate of patient 82 while resting, whilewalking, motion detector outputs while walking, etc. Such baselinephysiological parameters can be used to customize the WCD system, inorder to make its diagnoses more accurate, since the patients' bodiesdiffer from one another. Of course, such parameters can be stored in amemory of the WCD system, and so on.

A programming interface can be made according to embodiments, whichreceives such measured baseline physiological parameters. Such aprogramming interface may input automatically in the WCD system thebaseline physiological parameters, along with other data.

In embodiments, values of a first ECG signal are multiplied with valuesof a second ECG signal, in order to derive a product waveform. Theprocessing of such multiplying and other operations may be done byprocessor 230 or processor 330. Examples are now described.

FIG. 4 shows time diagrams using a single time axis 448. A diagram 419shows the amplitude of a first ECG signal A from a first vector on avertical semi-axis 417. The signal could be digitized, and its valuessampled quickly enough to where the depicted signal waveform appears asa continuous line in FIG. 4, which is good enough for purposes of thedescription of FIG. 4. First ECG signal A is shown as generalized—inthis instance as having upward-going peaks from a baseline value ofzero. Again, this generalization is good enough for purposes of thedescription of FIG. 4. The reason is that these peaks could be from trueECG features such as QRS complexes, or from noise.

FIG. 4 also shows a diagram 429 of a second ECG signal B from a secondvector, whose amplitude is shown against a vertical semi-axis 417. Thesame considerations apply as in diagram 419. From shared time axis 448,it will be appreciated that second ECG signal B is sensed substantiallycontemporaneously with when the first ECG signal was sensed.

In each of diagrams 419 & 429 taken by itself, processor 330 may not beable to discern whether an individual peak is generated from a true ECGfeature or from noise. For example, in diagram 419, each of peaks 461and 466 could be either from a true ECG feature of first ECG signal A,or from noise in the first channel that delivered first ECG signal A.The same applies also for peaks 471 & 476 in diagram 429, about secondECG signal B and the second channel that delivered second ECG signal B.

In embodiments, processors 230 and 330 discern the difference in whatgenerated the individual peaks of diagrams 419 and 429. And,disregarding peaks generated from noise, processors 230 and 330 may usepeaks generated by true ECG features to determine the value heart rate333. And that value alone may determine whether a rhythm is shockable ornot, regardless of whether the ECG features that generated these peaksare QRS complexes, which would be slower and at a lesser heart rate, orportions of the zig-zag of a VT or a VF waveform, which would be fasterand at a faster heart rate. Examples are now described.

FIG. 4 further shows a diagram 439, with a vertical semi-axis 437against time axis 448. Diagram 439 shows a product waveform that hasbeen generated according to embodiments by multiplying values of firstECG signal A with values of second ECG signal B. As such, the units ofvertical semi-axis 437 are voltage times voltage, or (Volts)². In otherwords, the product waveform of diagram 439 is not a depiction of an ECGsignal, or even of a voltage signal; rather, the product waveform ofdiagram 439 is a depiction of a useful construct according toembodiments.

The product waveform of diagram 439 has zero values where either firstECG signal A or second ECG signal B has a zero value. And, the productwaveform has non-zero values everywhere else. In addition, the productwaveform has tall peaks 431, 432, 433, 434, 435, which is where tallpeaks of first ECG signal A coincide substantially with tall peaks ofsecond ECG signal B. Moreover, the product waveform has short peaks 436where the peaks of first ECG signal A coincide only a little with thepeaks of second ECG signal B, or where one of these coincident peaks isnot tall.

In embodiments, peaks in diagram 439 that exceed a detection thresholdare detected in the product waveform. Such detection may be performed byprocessors 230, 330. For example, in diagram 439, a detection thresholdis shown by a line 498 that has a fixed value 497. Tall peaks 431, 432,433, 434, 435 exceed detection threshold 498, and are thus detected.Short peaks 436 do not exceed detection threshold 498, and are thus notdetected and disregarded. The detected tall peaks 431, 432, 433, 434,435 may be deemed to be generated from features of the patient's trueECG signal, which were transmitted from both channels, because the ECGsignal was the same in each channel. The short peaks 436 may bedisregarded because they are deemed to be generated from noise in thechannels, because noise may be generated independently in each channel,which means at different moments for each channel and with differentamplitudes for each channel. To the extent it is of interest to lookback at diagrams 419, 429, now it is known that peaks 461, 471 were froma true ECG feature, while peaks 466, 476 were from noise.

As seen on time axis 448, detected peaks 431, 432, 433, 434, 435 occurat times 441, 442, 443, 444, 445. In embodiments, time intervals aredefined between pairs of successive ones of the detected peaks. As such,time interval 451 is defined between peaks 431 & 432; time interval 452is defined between peaks 432 & 433; time interval 453 is defined betweenpeaks 433 & 434; and time interval 454 is defined between peaks 434 &435.

In embodiments, durations of these time intervals 451, 452, 453, 454 aremeasured, and a heart rate 333 of the patient is computed from thesemeasured durations. Such computing may be done by processor 230 orprocessor 330. Since detected peaks 431, 432, 433, 434, 435 aresubstantially evenly spaced in time, the computation of heart rate 333will be rather reliable.

In embodiments, it can be determined from the computed heart rate, orfrom a subsequent ECG signal, whether or not a shock criterion is met.For example, a fast heart rate may indicate VF or VT, and so on. If so,responsive to the shock criterion being met, discharge circuit 255 canbe controlled by processor 230 or 330 to discharge the stored electricalcharge through patient 82, while support structure 170 is worn bypatient 82 so as to deliver shock 111 to patient 82.

It may be observed that, determining heart rate 333 from tall peaks 431,432, 433, 434, 435 is similar to determining a heart rate from a seriesof QRS peaks. It should be remembered, however, that the productwaveform of time diagram is not an ECG signal—even the units of theamplitude are different.

It will be appreciated that the operations of FIG. 4 may happen in realtime. For example, the ECG signals of diagrams 419 and 429 may beacquired, optionally processed such as with high-pass-filtering andperhaps additional operations, and the product waveform may be computedagain in real time. Or, the signals may be stored, and then processed.

In the example of FIG. 4, the baseline value of diagrams 419 & 429 iszero. That is not, however, necessary for implementing the invention.Indeed, even if the baseline value were not zero, a similar phenomenonmay result. In particular, in the product waveform, the patient's ECGsignal being sensed concurrently in all the channels may generate tallerpeaks that can be useful for determining the heart rate, while noisegenerated independently in each channel may generate relatively shorterpeaks that can be disregarded.

While not necessary, it is preferred that the baseline value of diagrams419 & 429 be zero, since this may shorten the computations. Indeed,multiplying by zero results in zero, which requires lesser processing.As such, in some embodiments, processor 230, 330 is further configuredto high-pass filter at least one or both of first ECG signal A andsecond ECG signal B, so as to derive a high-pass filtered first ECGsignal, and a high-pass filtered second ECG signal. In such embodiments,the product waveform may be derived by multiplying values of thehigh-pass filtered first ECG signal instead of multiplying values of thefirst ECG signal, and so on with the second signal. A good value for thehigh-pass filtering is 8 Hz. In those instances, what is shown indiagrams 419, 429 would be high-pass filtered versions of the ECGsignals, instead of the ECG signals themselves.

The examples of FIG. 4 were shown with generalized ECG signals. Examplesare now given with non-generalized ECG signals.

FIG. 5A is a time diagram of two sample noise-free ECG signals 501, 502from two different vectors, superimposed according to embodiments. FIG.5B is a time diagram of noisy versions 519, 529 of ECG signals 501, 502.Noisy ECG signals 519, 529 are shown on the same axis, which isdifferent from FIG. 4 that shows these signals in separate diagrams 419,429.

FIG. 5C is a time diagram 539 of a product waveform of the ECG signalsof FIG. 5B according to embodiments. It will be appreciated that thisproduct waveform has at least three tall peaks 531, 532, 533 that aresubstantially evenly spaced in time. Moreover, this product waveform hasshort peaks 536, which can be ignored. In addition, this productwaveform has a spurious tall peak 530 that is not part of the evenlyspaced pattern; one can tell by inspection that peak 530 is noise thatmay complicate the processor's computation of heart rate 333. Spurioustall peak 530 may have arisen in a number of ways. One such way is froma noise event at a single electrode that affected similarly the ECGsignals in two channels, if these two ECG signals are the ones beingmultiplied for this product waveform.

FIG. 6A is a time diagram of two sample noise-free ECG signals 601, 602from another two different vectors, superimposed according toembodiments. FIG. 6B is a time diagram of noisy versions 619, 629 of ECGsignals 601, 602, shown on the same axis. FIG. 6C is a time diagram 639of a product waveform of the ECG signals of FIG. 6B according toembodiments. It will be appreciated that this product waveform has atleast three tall peaks 631, 632, 633 that are substantially evenlyspaced. Moreover, this product waveform has short peaks 636, which canbe ignored.

In some embodiments, product waveforms can be made from ECG signals ofmore than two vectors or channels, for amplified effect. For example,the electrodes may further define additional vectors, such as a thirdvector, a fourth vector and so on. In such embodiments, measurementcircuits 220, 320 can be further configured to sense a third ECG signalfrom the third vector, a fourth ECG signal from the fourth vector, andso on. Moreover, processors 230, 330 can be further configured tomultiply values of the third ECG signal with the values of the first ECGsignal and of the second ECG signal to derive the product waveform. Insuch a case, the product waveform may be made from three ECG signals,not just two.

Moreover, processor 230, 330 can be further configured to multiplyvalues of the fourth ECG signal with the values of the first ECG signal,of the second ECG signal and of the third ECG signal, to derive theproduct waveform. In such a case, the product waveform may be made fromfour ECG signals, not just three.

An example of using more than two ECG signals to derive a productwaveform is now described. FIG. 13 is a diagram of the amplitudes ofvarious ECG signals against a time axis 1348, which has events in twotime domains 1341, 1342. ECG signals 1321, 1322, 1323, 1324 from fourchannels are shown, which could be taken from signals 419, 429, 519,529, 619, 629. In the first time domain 1341, these ECG signals 1321,1322, 1323, 1324 are substantially concurrent, and are multipliedtogether to generate a product waveform 1339.

In FIG. 13, the contingency is that the patient suffers SCA during thesecond time domain 1342. At that time, a subsequent ECG signal 1352 issensed, and a diagnosis is made. A person skilled in the art willrecognize that ECG signal 1352 likely denotes VF or VT, which calls fordefibrillation. ECG signal 1352 could be sensed from any of the channelsthat generated these ECG signals 1321, 1322, 1323, 1324, or another ECGsignal; here ECG signal 1352 is shown as being from the same channel asECG signal 1322, but that is only by way of example. And, artificially,FIG. 13 does not show the ECG signals sensed by the other channelsduring subsequent time domain 1342; if these had been also shown, theywould show a pattern similar to that of ECG signal 1352. Plus, the VT orVF of second time domain 1342 can also be sensed by the product waveformof the ECG signals from two or more of the channels. During time domain1342, however, sensing ECG signal 1352 from a single ECG channel may beenough, because the patient may be motionless, and much source of ECGnoise may no longer be present.

An example of the amplified effect of using more than two ECG signals toderive the product waveform is now described. FIG. 7 is a time diagram739 of the product waveform that can be derived by multiplying theproduct waveform of FIG. 5C with the product waveform of FIG. 6C. Assuch, the product waveform of time diagram 739 is from four distinctchannels.

It will be observed that time diagram 739 has at least three tall peaks731, 732, 733 that are substantially evenly spaced in time, and shortpeaks 736 that can be disregarded in the computation of heart rate 333.This aspect is similar with the product waveforms of FIGS. 5C and 6C,each of which was made from only two ECG signals.

It will be appreciated that the product waveform of FIG. 7 is improvedover those of FIG. 5C and FIG. 6C. These improvements make it easier todistinguish the valid peaks from the peaks to disregard, for computingheart rate 333.

One improvement is that the product waveform of diagram 739 has nospurious tall peaks, of the type of peak 530 in FIG. 5C.

Another improvement is in the ratio of the amplitude of tall peaks 731,732, 733 over short peaks 736. This ratio is larger in FIG. 7 than inFIGS. 5C and 6C. In other words, in FIG. 7 the usable tall peaks becametaller while the short peaks became shorter, which is a phenomenon thatmakes them even easier to differentiate from each other and ultimatelydiscard the short peaks.

One more improvement is that tall peaks 731, 732, 733 are narrower.There are fewer peaks of medium height immediately before andimmediately after the very tall peaks. Such medium-height peaks mightintroduce ambiguity in the detection of when the tall peak occurred. Thefewer the medium-height peaks, the less ambiguity will there be in suchdetection, because it will be easier to set the detection threshold.

Detection is now described in more detail. In some embodiments, when apeak is detected at a certain moment, no other peaks are detected for aninactive time period after the certain moment. An example is nowdescribed.

FIG. 8 is a time diagram 839, which uses a time axis 848 and a verticalsemi-axis 837. Time diagram 839 depicts another product waveform. While,however, it was mentioned with reference to FIG. 4 that a signalwaveform appears as a continuous line and that was good enough for FIG.4, for the detection of FIG. 8 granularity may start to appear due tofine sampling. Even when it does, this recognition is not a problem. So,the product waveform in time diagram 839 has three tall peak groups 831,832, 833, and multiple small peaks 836. The granularity is that each ofpeak groups 831, 832, 833 actually has multiple tall peaks due to thefine sampling.

In diagram 839, a detection threshold is shown by a line 898 that has afixed value 897. Short peaks 836 do not exceed detection threshold 898,and are thus not detected and disregarded. For the taller peaks, adetection event happens at detection point 851, when the first tall peakof peak group 831 exceeds value 897. After detection point 851,detection is disabled for an inactive time period 899, during which noother peak is detected. As such, none of the other peaks of peak group831 are detected, and the whole peak group 831 is detected only once.Similarly, another detection event happens at detection point 852, whenthe first tall peak of peak group 832 exceeds value 897. Detection point852 is followed by another inactive time period 899. And one moredetection event happens at detection point 853, when the first tall peakof peak group 833 exceeds value 897. Detection point 853 is followed byanother inactive time period 899.

In FIG. 8, detection points 851, 852, 853 happen at respective timemoments 841, 842, 843. Heart rate 333 can then be computed fromdurations between time moments 841, 842, 843. It is preferred to set theduration of inactive time period 899 to be short enough so as to notinterfere with expected values of the heart rate.

In FIG. 8, detection threshold 898 was constant. In fact, it was at agood value 897, given what needs to be detected and what needs to bediscarded. Good such values may be learned with time. In someembodiments, however, the detection threshold may change with time,dynamically, in anticipation of the amplitude and timing of the nextpeak that should be detected. In some embodiments, responsive to acertain one of the peaks being thus detected, a certain amplitude of thecertain detected peak is input in the processor, for example in a memoryregister and so on. In such embodiments, the detection threshold can bethen established for later use responsive to the input certainamplitude. Examples of such embodiments are now described.

FIG. 9 is a time diagram 939, which uses a time axis 948 and a verticalsemi-axis 937. Time diagram 939 depicts one more product waveform, whichhas three tall peak groups 931, 932, 933, and multiple small peaks thatare disregarded.

In diagram 939, a detection threshold is shown by a line 998 whose valuechanges with time. The value starts with a fixed value 997 until adetection event happens at detection point 951, which is from the firsttall peak of peak group 931. At that time, a certain amplitude of thecertain detected peak is input. That certain amplitude is shown as avalue at a height 935, with a very short horizontal line. Then aninactive time period 999 follows. At the end of this inactive timeperiod, the detection threshold 998 is then established responsive tothe input certain amplitude. As such, it becomes initially establishedat a value 996, which is determined from the value at height 935. Thendetection threshold 998 can drop exponentially, until it reaches a lowervalue and stay at that lower value. The lower value can be, for example,a fraction of value 996. While at that lower value, a detection eventhappens at detection point 952, which may be followed by anotherinactive time period 999, then resetting the detection threshold 998 ata higher value, and so on. One more detection event happens at detectionpoint 953. Detection points 951, 952, 953 happen at respective timemoments 941, 942, 943. Heart rate 333 can then be computed fromdurations between time moments 941, 942, 943, as per the above.

More refinements are now described. FIG. 10 shows a section of a patient1082 having a heart 1085. In FIG. 10, patient 1082 is viewed from thetop, and is facing down. Given this orientation, heart 1085 is on theright hand side within the torso. A measurement circuit 1020 and aprocessor 1030 can be made as described for measurement circuits 220,320 and for processors 230, 330. Processor 1030 may further computeheart rate 333 according to embodiments.

Patient 1082 is wearing a support structure, which is not shown in FIG.10 for simplicity. The support structure attaches or applies fourelectrodes 1091, 1092, 1093, 1094 to different locations of the torso ofpatient 1082. Each electrode may have a wire lead, which leads tomeasurement circuit 1020. One of these wire leads is shown as wire lead1005. Any pair of electrodes 1091, 1092, 1093, 1094 defines a vector,across which an ECG signal may be sensed or measured. The discussion forFIG. 10 is only for vectors 1011, 1012, 1015, 1016.

Heart 1085 is the source of the ECG signal. Because electrodes 1092 &1093 are near the source of the ECG signal, and electrodes 1091 & 1094are away from the heart, the QRS morphologies of ECG signals sensed ormeasured between vectors 1011, 1012, 1015, 1016 can be both similar andalso synchronized. These aspects, namely similarity in morphology andsynchronization, can increase the amplitude of the tall peaks in aproduct waveform.

In some embodiments, the ECG signals might not start out assynchronized. In such embodiments, one of the signals is time-shiftedwith respect to the other to derive a time-shifted ECG signal, and theproduct waveform is derived by multiplying values of the time-shiftedECG signal instead of multiplying values of the ECG signal before it wastime shifted. An example is now described.

FIG. 11 shows time diagrams across a time axis 1148. A diagram 1119 hasa vertical amplitude semi-axis 1117, and shows the waveform of anidealized, noise-free first ECG signal A. ECG signal A is centeredaround a baseline BL, and has three QRS complexes 1161, 1162, 1163.

In addition, a diagram 1126 has a vertical amplitude semi-axis 1127, andshows the waveform of an idealized, noise-free second ECG signal B. ECGsignal B is centered around a baseline BL, and has three QRS complexes1171, 1172, 1173. It will be observed that second ECG signal B isdelayed with respect to first ECG signal A by a time lag 1170. The timelag may arise due to the vectors having differing distances from theheart, and so on.

As mentioned above, processors 230, 330, 1030 may be configured totime-shift second ECG signal B with respect to first ECG signal A, so asto derive a time-shifted second ECG signal. For example, one morediagram 1129 in FIG. 11 repeats semi-axis 1127. In addition, it shows abox 1178 that repeats the portion of the signal of diagram 1126 thatincludes QRS complexes 1171, 1172, 1173. In addition, in diagram 1129box 1178 is shifted by an amount 1177 that is equal to time lag 1170. Assuch, in diagram 1129 the time lag 1170 is corrected. Now a productwaveform can be derived by multiplying values of the time-shifted secondECG signal of diagram 1129, instead of multiplying values of the sensedsecond ECG signal 1126.

The time-shifting may be embedded in the programming of processor 230 or330 or 1030, at the time that a patient is fitted. At that time the ECGsignals can be free from noise. In particular, in some embodiments,processor 230 or 330 or 1030 can be further configured to detect a firsttest peak 1161 occurring in first ECG signal A, detect a second testpeak 1171 occurring in second ECG signal B, and detect a time lag 1170between first test peak 1161 and second test peak 1171. In suchembodiments, second ECG signal B can be time-shifted according to timelag 1170 that was learned this way.

The devices and/or systems mentioned in this document perform functions,processes and/or methods. These functions, processes and/or methods maybe implemented by one or more devices that include logic circuitry. Sucha device can be alternately called a computer, and so on. It may be astandalone device or computer, such as a general purpose computer, orpart of a device that has one or more additional functions. The logiccircuitry may include a processor and non-transitory computer-readablestorage media, such as memories, of the type described elsewhere in thisdocument. Often, for the sake of convenience only, it is preferred toimplement and describe a program as various interconnected distinctsoftware modules or features. These, along with data are individuallyand also collectively known as software. In some instances, software iscombined with hardware, in a mix called firmware.

Moreover, methods and algorithms are described below. These methods andalgorithms are not necessarily inherently associated with any particularlogic device or other apparatus. Rather, they are advantageouslyimplemented by programs for use by a computing machine, such as ageneral-purpose computer, a special purpose computer, a microprocessor,a processor such as described elsewhere in this document, and so on.

This detailed description includes flowcharts, display images,algorithms, and symbolic representations of program operations within atleast one computer readable medium. An economy is achieved in that asingle set of flowcharts is used to describe both programs, and alsomethods. So, while flowcharts described methods in terms of boxes, theyalso concurrently describe programs.

Methods are now described.

FIG. 12 shows a flowchart 1200 for describing methods according toembodiments. According to an operation 1210, a first ECG signal from afirst vector and a second ECG signal from the second vector may besensed or measured. The second ECG signal may be sensed substantiallycontemporaneously with sensing the first ECG signal. Sensing may beperformed by electrodes, etc.

According to another, optional operation 1220, the first ECG signaland/or the second ECG signal may be high-pass filtered, to derive ahigh-pass filtered first ECG signal and/or a high-pass filtered secondECG signal.

According to another operation 1230, values of the first ECG signal maybe multiplied with values of the second ECG signal to derive a productwaveform. If optional operation 1220 has been performed, then theproduct waveform may be derived by multiplying values of the high-passfiltered first ECG signal instead of multiplying values of the first ECGsignal, and so on with the second ECG signal.

According to another operation 1240, peaks may be detected in theproduct waveform, which exceed a detection threshold. The detectionthreshold may be as described above.

According to another operation 1250, durations may be measured, of timeintervals between pairs of successive ones of the detected peaks. Samplesuch durations are durations 451-454 of FIG. 4.

According to another operation 1260, a heart rate of the patient may becomputed. Computing may be from the measured durations of the timeintervals, as described above. The computed heart rate may be stored inmemory 238. Optionally the computed heart rate may be transmittedwirelessly by communication module 290. Optionally the computed heartrate may be displayed by a screen that implements user interface 280.

According to another, optional operation 1262, the heart rate computedat operation 1260 may be transmitted. Transmitting may be performed, forexample, wirelessly by communication module 290.

According to another, optional operation 1264, the heart rate computedat operation 1260 may be displayed. Displaying may be performed, forexample, by a screen of user interface 280.

According to another operation 1270, a subsequent ECG signal may besensed after sensing the first ECG signal. The subsequent ECG signal maybe sensed from any vector. Sensing may be performed by electrodes, etc.Of course, the ECG signal from either the first vector or the secondvector may be considered to have a) an early portion that is consideredto be the first or second ECG signal for operation 1230, and b) asubsequent portion that is considered to be the subsequent ECG signal.The subsequent signal may have less noise, for example be more similarto signal 501 than to the signal of diagram 419.

According to another operation 1280, it may be determined whether or nota shock criterion is met. The determination may be from the subsequentECG signal or from the computed heart rate. The determination may beperformed responsive to the value of the heart rate computed atoperation 1260. If at operation 1280 the answer is “NO”, indicated by acrossed-out mark, then execution may return to a previous operation,such as operation 1210.

If at operation 1280 the answer is “YES”, indicated by a checkmark, thenaccording to another operation 1290, responsive to the shock criterionbeing met the discharge circuit may be controlled to discharge thestored electrical charge through the patient. Discharging may be whilethe support structure is worn by the patient, so as to deliver a shockto the patient.

In the methods described above, each operation can be performed as anaffirmative act or operation of doing, or causing to happen, what iswritten that can take place. Such doing or causing to happen can be bythe whole system or device, or just one or more components of it. Itwill be recognized that the methods and the operations may beimplemented in a number of ways, including using systems, devices andimplementations described above. In addition, the order of operations isnot constrained to what is shown, and different orders may be possibleaccording to different embodiments. Examples of such alternate orderingsmay include overlapping, interleaved, interrupted, reordered,incremental, preparatory, supplemental, simultaneous, reverse, or othervariant orderings, unless context dictates otherwise. Moreover, incertain embodiments, new operations may be added, or individualoperations may be modified or deleted. The added operations can be, forexample, from what is mentioned while primarily describing a differentsystem, apparatus, device or method.

A person skilled in the art will be able to practice the presentinvention in view of this description, which is to be taken as a whole.Details have been included to provide a thorough understanding. In otherinstances, well-known aspects have not been described, in order to notobscure unnecessarily this description.

Some technologies or techniques described in this document may be known.Even then, however, it does not necessarily follow that it is known toapply such technologies or techniques as described in this document, orfor the purposes described in this document.

This description includes one or more examples, but this fact does notlimit how the invention may be practiced. Indeed, examples, instances,versions or embodiments of the invention may be practiced according towhat is described, or yet differently, and also in conjunction withother present or future technologies. Other such embodiments includecombinations and sub-combinations of features described herein,including for example, embodiments that are equivalent to the following:providing or applying a feature in a different order than in a describedembodiment; extracting an individual feature from one embodiment andinserting such feature into another embodiment; removing one or morefeatures from an embodiment; or both removing a feature from anembodiment and adding a feature extracted from another embodiment, whileproviding the features incorporated in such combinations andsub-combinations.

In general, the present disclosure reflects preferred embodiments of theinvention. The attentive reader will note, however, that some aspects ofthe disclosed embodiments extend beyond the scope of the claims. To therespect that the disclosed embodiments indeed extend beyond the scope ofthe claims, the disclosed embodiments are to be considered supplementarybackground information and do not constitute definitions of the claimedinvention.

In this document, the phrases “constructed to” and/or “configured to”denote one or more actual states of construction and/or configurationthat is fundamentally tied to physical characteristics of the element orfeature preceding these phrases and, as such, reach well beyond merelydescribing an intended use. Any such elements or features can beimplemented in a number of ways, as will be apparent to a person skilledin the art after reviewing the present disclosure, beyond any examplesshown in this document.

Any and all parent, grandparent, great-grandparent, etc. patentapplications, whether mentioned in this document or in an ApplicationData Sheet (“ADS”) of this patent application, are hereby incorporatedby reference herein as originally disclosed, including any priorityclaims made in those applications and any material incorporated byreference, to the extent such subject matter is not inconsistentherewith.

In this description a single reference numeral may be used consistentlyto denote a single item, aspect, component, or process. Moreover, afurther effort may have been made in the drafting of this description touse similar though not identical reference numerals to denote otherversions or embodiments of an item, aspect, component or process thatare identical or at least similar or related. Where made, such a furthereffort was not required, but was nevertheless made gratuitously so as toaccelerate comprehension by the reader. Even where made in thisdocument, such a further effort might not have been made completelyconsistently for all of the versions or embodiments that are madepossible by this description. Accordingly, the description controls indefining an item, aspect, component or process, rather than itsreference numeral. Any similarity in reference numerals may be used toinfer a similarity in the text, but not to confuse aspects where thetext or other context indicates otherwise.

The claims of this document define certain combinations andsubcombinations of elements, features and acts or operations, which areregarded as novel and non-obvious. Additional claims for other suchcombinations and subcombinations may be presented in this or a relateddocument. These claims are intended to encompass within their scope allchanges and modifications that are within the true spirit and scope ofthe subject matter described herein. The terms used herein, including inthe claims, are generally intended as “open” terms. For example, theterm “including” should be interpreted as “including but not limitedto,” the term “having” should be interpreted as “having at least,” etc.If a specific number is ascribed to a claim recitation, this number is aminimum but not a maximum unless stated otherwise. For example, where aclaim recites “a” component or “an” item, it means that it can have oneor more of this component or item.

In construing the claims of this document, the inventor(s) invoke 35U.S.C. § 112(f) only when the words “means for” or “steps for” areexpressly used in the claims. Accordingly, if these words are not usedin a claim, then that claim is not intended to be construed by theinventor(s) in accordance with 35 U.S.C. § 112(f).

What is claimed is:
 1. A wearable cardioverter defibrillator (WCD)system, comprising: a support structure configured to be worn by anambulatory patient; an energy storage module configured to store anelectrical charge; a discharge circuit coupled to the energy storagemodule; electrodes configured to be attached at different locations ofthe patient's body so as to define at least a first vector and a secondvector distinct from the first vector; a measurement circuit configuredto sense a first Electrocardiogram (ECG) signal from the first vector, asecond ECG signal from the second vector substantially contemporaneouslywith sensing the first ECG signal, and a subsequent ECG signal aftersensing the first ECG signal; and a processor configured to: multiplyvalues of the first ECG signal with values of the second ECG signal toderive a product waveform, detect, in the product waveform, peaks thatexceed a detection threshold, measure durations of time intervalsbetween pairs of successive ones of the detected peaks, compute a heartrate of the patient from the measured durations of the time intervals,determine from the subsequent ECG signal whether or not a shockcriterion is met, and control, responsive to the shock criterion beingmet, the discharge circuit to discharge the stored electrical chargethrough the patient while the support structure is worn by the patientso as to deliver a shock to the patient; and a communication moduleconfigured to transmit wirelessly the computed heart rate.
 2. The WCDsystem of claim 1, further comprising: a screen configured to displaythe computed heart rate.
 3. The WCD system of claim 1, in which thefirst ECG signal is high-pass filtered to derive a high-pass filteredfirst ECG signal, and the product waveform is derived by multiplyingvalues of the high-pass filtered first ECG signal instead of multiplyingvalues of the first ECG signal.
 4. The WCD system of claim 1, in whichthe electrodes further define a third vector, the measurement circuit isfurther configured to sense a third ECG signal from the third vector,and the processor is further configured to: multiply values of the thirdECG signal with the values of the first ECG signal and of the second ECGsignal to derive the product waveform.
 5. The WCD system of claim 4, inwhich the electrodes further define a fourth vector, the measurementcircuit is further configured to sense a fourth ECG signal from thefourth vector, and the processor is further configured to: multiplyvalues of the fourth ECG signal with the values of the first ECG signal,of the second ECG signal and of the third ECG signal, to derive theproduct waveform.
 6. The WCD system of claim 1, in which when a peak isdetected at a certain moment, no other peaks are detected for aninactive time period after the certain moment.
 7. The WCD system ofclaim 1, in which the detection threshold changes with time.
 8. The WCDsystem of claim 1, in which responsive to a certain one of the peaksbeing thus detected, a certain amplitude of the certain detected peak isinput, and the detection threshold is then established responsive to theinput certain amplitude.
 9. The WCD system of claim 1, in which thesecond ECG signal is time-shifted with respect to the first ECG signalto derive a time-shifted second ECG signal, and the product waveform isderived by multiplying values of the time-shifted second ECG signalinstead of multiplying values of the sensed second ECG signal.
 10. TheWCD system of claim 9, in which the processor is further configured to:detect a first test peak occurring in the first ECG signal, detect asecond test peak occurring in the second ECG signal, detect a time lagbetween the first test peak and the second test peak, and in which thesecond ECG signal is time-shifted according to the time lag.
 11. Awearable cardioverter defibrillator (WCD) system, comprising: a supportstructure configured to be worn by an ambulatory patient; an energystorage module configured to store an electrical charge; a dischargecircuit coupled to the energy storage module; electrodes configured tobe attached at different locations of the patient's body so as to defineat least a first vector and a second vector distinct from the firstvector; a measurement circuit configured to sense a firstElectrocardiogram (ECG) signal from the first vector, a second ECGsignal from the second vector substantially contemporaneously withsensing the first ECG signal, and a subsequent ECG signal after sensingthe first ECG signal; a processor configured to: multiply values of thefirst ECG signal with values of the second ECG signal to derive aproduct waveform, detect, in the product waveform, peaks that exceed adetection threshold, measure durations of time intervals between pairsof successive ones of the detected peaks, compute a heart rate of thepatient from the measured durations of the time intervals, determinefrom the subsequent ECG signal whether or not a shock criterion is met,and control, responsive to the shock criterion being met, the dischargecircuit to discharge the stored electrical charge through the patientwhile the support structure is worn by the patient so as to deliver ashock to the patient; and a screen configured to display the computedheart rate.
 12. The WCD system of claim 11, in which the first ECGsignal is high-pass filtered to derive a high-pass filtered first ECGsignal, and the product waveform is derived by multiplying values of thehigh-pass filtered first ECG signal instead of multiplying values of thefirst ECG signal.
 13. The WCD system of claim 11, in which theelectrodes further define a third vector, the measurement circuit isfurther configured to sense a third ECG signal from the third vector,and the processor is further configured to: multiply values of the thirdECG signal with the values of the first ECG signal and of the second ECGsignal to derive the product waveform.
 14. The WCD system of claim 13,in which the electrodes further define a fourth vector, the measurementcircuit is further configured to sense a fourth ECG signal from thefourth vector, and the processor is further configured to: multiplyvalues of the fourth ECG signal with the values of the first ECG signal,of the second ECG signal and of the third ECG signal, to derive theproduct waveform.
 15. The WCD system of claim 11, in which when a peakis detected at a certain moment, no other peaks are detected for aninactive time period after the certain moment.
 16. The WCD system ofclaim 11, in which the detection threshold changes with time.
 17. TheWCD system of claim 11, in which responsive to a certain one of thepeaks being thus detected, a certain amplitude of the certain detectedpeak is input, and the detection threshold is then establishedresponsive to the input certain amplitude.
 18. The WCD system of claim11, in which the second ECG signal is time-shifted with respect to thefirst ECG signal to derive a time-shifted second ECG signal, and theproduct waveform is derived by multiplying values of the time-shiftedsecond ECG signal instead of multiplying values of the sensed second ECGsignal.
 19. The WCD system of claim 18, in which the processor isfurther configured to: detect a first test peak occurring in the firstECG signal, detect a second test peak occurring in the second ECGsignal, detect a time lag between the first test peak and the secondtest peak, and in which the second ECG signal is time-shifted accordingto the time lag.
 20. A non-transitory computer-readable storage mediumstoring one or more programs which, when executed by at least oneprocessor of a wearable cardioverter defibrillator (“WCD”) system, theWCD system further including a support structure configured to be wornby an ambulatory patient, an energy storage module that can store anelectrical charge, a discharge circuit coupled to the energy storagemodule, electrodes attached at different locations of the patient's bodyso as to define at least a first vector and a second vector distinctfrom the first vector, and a measurement circuit, these one or moreprograms result in operations comprising: sensing, by the electrodes, afirst Electrocardiogram (ECG) signal from the first vector; sensing asecond ECG signal from the second vector substantially contemporaneouslywith sensing the first ECG signal; multiplying values of the first ECGsignal with values of the second ECG signal to derive a productwaveform; detecting, in the product waveform, peaks that exceed adetection threshold; measuring durations of time intervals between pairsof successive ones of the detected peaks; computing a heart rate of thepatient from the measured durations of the time intervals; sensing asubsequent ECG signal after sensing the first ECG signal; determiningfrom the subsequent ECG signal whether or not a shock criterion is met;and controlling, responsive to the shock criterion being met, thedischarge circuit to discharge the stored electrical charge through thepatient while the support structure is worn by the patient so as todeliver a shock to the patient.
 21. A method for a wearable cardioverterdefibrillator (WCD) system, the WCD system including a support structureconfigured to be worn by an ambulatory patient, an energy storage modulestoring an electrical charge, a discharge circuit coupled to the energystorage module, electrodes attached at different locations of thepatient's body so as to define at least a first vector and a secondvector distinct from the first vector, a measurement circuit and aprocessor, the method comprising: sensing, by the electrodes, a firstElectrocardiogram (ECG) signal from the first vector; sensing a secondECG signal from the second vector substantially contemporaneously withsensing the first ECG signal; multiplying values of the first ECG signalwith values of the second ECG signal to derive a product waveform;detecting, in the product waveform, peaks that exceed a detectionthreshold; measuring durations of time intervals between pairs ofsuccessive ones of the detected peaks; computing a heart rate of thepatient from the measured durations of the time intervals; sensing asubsequent ECG signal after sensing the first ECG signal; determiningfrom the subsequent ECG signal whether or not a shock criterion is met;and controlling, responsive to the shock criterion being met, thedischarge circuit to discharge the stored electrical charge through thepatient while the support structure is worn by the patient so as todeliver a shock to the patient.